1. Field of the Invention
The present invention relates to multiphase DC-to-DC switching power converters and, more particularly, to a multiphase DC-to-DC switching power converter with leading edge and cross channel blanking.
2. Description of the Related Art
A DC-to-DC switching power converter is a device that converts one DC voltage to another DC voltage with very little power loss. A buck converter is one type of DC-to-DC switching power converter that receives an input voltage of one polarity, and generates an output voltage of the same polarity that is lower than the input voltage.
A buck converter utilizes a pulse width modulated (PWM) signal to turn a power MOS transistor on and off. When the power MOS transistor is turned on, a current flows from the power MOS transistor through an inductor to a capacitor and a load. When the power MOS transistor is turned off, a current flows from ground through a diode and the inductor to the capacitor and the load.
The output voltage across the capacitor has a value approximately equal to the duty cycle of the PWM signal multiplied times the input voltage. For example, a PWM signal with a 10% duty cycle input to a buck converter with a 12V input voltage produces an output voltage of approximately 1.2V.
A synchronous buck converter is a buck converter where the diode has been replaced with another MOS transistor, which is also referred to as a synchronous MOS rectifier. The combination of the power MOS transistor and the synchronous MOS rectifier is often referred to as a half bridge. A multiphase synchronous buck converter is a multichannel buck converter that includes two or more substantially-identical synchronous buck converter circuits that are driven out of phase.
For example, a two-phase synchronous buck converter is a two-channel buck converter that includes two identical synchronous buck converter circuits that share a common capacitor, with power MOS transistors that are driven 180° out of phase. A multiphase, multi-output synchronous buck converter utilizes different buck converter channels from the same or different input supply voltages. This can be integrated on the same silicon substrate, and is often driven out of phase from one another.
Buck converters often use current sense circuits to measure the magnitude of the current that flows through either the power MOS transistor or the synchronous MOS transistor. The current measurement can be used for a variety of purposes. For example, with peak current control, the current measurement can be used directly or indirectly to control the timing of the falling edge of a PWM signal, which turns off the power MOS transistor.
One problem with sensing the current that flows through a power MOS transistor or a synchronous MOS transistor is that as the MOS transistor turns on, circuit parasitics (both substrate level and board level, such as package lead inductance), high current gate drive pulses, and other factors can create a significant noise spike on the leading edge of a current sense signal that represents the current that flows through the MOS transistor. This noise can cause faulty current measurements which, in turn, can lead to improper circuit operation.
One approach to overcoming this problem is known as leading-edge blanking. With leading-edge blanking, the current sense signal is blanked (e.g., held to ground) for a specific amount of time while the MOS transistor is initially turned on. The specific amount of time corresponds with the width of the noise spike on the leading edge of the current sense signal.